The machines currently in use for packaging single articles of substantially rectangular shape, or more frequently for wrapping groups of individual articles comprising, as a rule, containers for consumables in general and in particular food products and the like of a unit having rectangular shape, subsequently referred to as articles, with heat-shrinking material, and includes automatic machines with an intermediate or continuous movement which are designed on the basis of multiple modes for wrapping the heat-shrinking material around the individual articles to be wrapped.
In accordance with this known wrapping machines it is usual to wrap the article to be wrapped in the direction in which it is moving using the heat-shrinking sheet material in such a way that the material extends beyond the two opposite sides of the article and then the whole assembly is passed through a tunnel stove to cause the material to adhere by heat-shrinking to the wrapped sides and to the two opposite sides of the article before folding the corresponding material onto the latter sides.
Some known machines for wrapping such individual articles which are caused to advance in a continuous succession in an intermittently equally spaced arrangement or in a continuous manner use two sheets of the heat-shrinking material which are rhythmically passed above and below two successive articles respectively in a sealing station where they are transversely joined together by welding and then cut so as to close off or seal progressively the enclosure or wrapping for a preceding article and respectively join the sheets for wrapping of the next article
Articles so wrapped are then caused to advance through a tunnel stove to cause the material to adhere by heat-shrinking to the wrapped sides and to the opposite sides of the corresponding article after the corresponding surplus material has been folded up against the latter two sides (see for example U.S. Pat. Nos. 3,869,844 and 3,927,507).
Other known machines for packaging the articles which are caused to advance in an equidistant arrangement with continuous movement provide for the use of a single sheet of the heat-shrinking material.
One type of these latter known machines provides the sheet to be fed parallel to the direction of movement of the longitudinally equally spaced articles and folds it as it advances in a tubular shape with its corresponding longitudinal edges overlapped around the advanced articles with the overlapped edges to be joined by heat welding.
The articles so wrapped or enclosed in the tubular shape of sheet are then caused to pass their continuous movement first through a first station or first tunnel stove for a first heat-shrinking of the material around the articles, and then, upon leaving the first station, through a second station to cut the sheet in tubular form between two successive articles, so that there is surplus material all around the posterior and anterior sides between two successive articles, and finally through a third station or second tunnel stove to complete the action by causing the material to adhere by heat-shrinking to the wrapped sides and to the anterior and posterior sides of the same article after the corresponding material has been folded up against these latter sides (see GB no. 1,382,842).
Still another known machines use only one sheet for wrapping articles which are caused to advance in an equally spaced arrangement with continuous movement provide the sheet to be fed from the top in such a way as to extend it over the articles in such a way so as to overlap the two opposing lateral sides, and to carry it, drawing from the corresponding spool downwards in a loop folded form between successive articles in order to thrust it in the direction of movement of the articles beneath the previous articles where the looped portion is cut thereby producing two ends or edges of wrapping material which are posterior for the preceding article and anterior for the immediately following article.
In the course of the continuous movement of the articles the edges corresponding to each article are caused to overlap each other on the lower or bottom side of the article and then, while continuing their movements, the articles so wrapped are successively placed within a tunnel stove to cause the wrapping material to adhere by heat-shrinking in the usual way to the wrapped sides and the two opposite sides of the article after the corresponding material has been folded against the latter two sides (see GB patent No. 1,355,571).
From the known art in the field of packaging it is already known how sheets or pieces of packaging material cut from a sheet delivered from a feed spool across the path of articles to be packed can be provided in a continuous movement in such a way as to become folded in a horizontal U-shape against the anterior side and the two upper and lower parallel sides of the article adjacent thereto with the terminal parts of the arms of the U-shape extending beyond the posterior side and then fold the terminal parts onto the latter side where they are joined or sealed together when partly overlapped.
The means provided to implement this form of packaging normally comprise at least two pairs of opposing belt means performing a closed movement to carry the longitudinal edges of the said sheets to convey them across the direction of movement of the objects being packed (see GB patent 1,037,261 and U.S. Pat. No. 2,424,406), or by only two of the means in closed movement located respectively at the longitudinal edges so as to hold them by suction (see GB patent 958,377 and U.S. Pat. No. 2,871,257).
The machines which use the latter method of U-shaped bending of the packaging material with final folding and joining of the edges of the sheets by sealing on the posterior side of the articles being wrapped require complicated devices both for this last folding and for sealing. As a result, these machines for the wrapping of articles with heat-shrinking material which already have a tunnel stove to cause the material to adhere to the articles by heat-shrinking of the heat-shrinking material which is therefore also heat-weldable, it is preferred, if not directly expedient require the method having steps of first folding the heat-shrinking material around the anterior, upper and posterior sides of the article with an overturned U-fold and then refolding the terminal parts of the U-shaped onto the bottom side of the article with partial overlap.
Unseccessful attempts have been made to eliminate the complicated bending and sealing arrangements for the edges on the posterior side of products using the heat source of the tunnel stove to effect joining and sealing of the overlapping parts of the edges of the U-shape wrapping material on the lower side of the articles. The action of the stove causing the heat-shrinking packaging material to adhere to the product by heat-shrinking and therefore providing greater flexibility, i.e. a greater productive output per unit time and a more economic cost for wrapping with these machines using the heat-shrinking material, in practice has not made it possible to pursue an improved machines because of the complexity of the mechanisms used to achieve folding and overlapping of the aforesaid terminal parts of the edges of the U-shaped material turned over the lower side of the articles (see for example aforesaid GB no. 1,355,571).
This drawback has been eliminated. Applicant's Italian patent No. 1,169,175 of the 23 Feb. 1983 proposing and subsequently constructing a machine for the wrapping of articles fed in an equally spaced succession by means of a continuously moving conveyor with sheets cut progressively from a sheet of heat-shrinking material extending beyond the two lateral sides of the articles and then subsequently moved by suction holding means along the corresponding longitudinal edges across the direction of advance of the individual successive articles so as to be folded onto the anterior, superior and inferior faces of a corresponding article in a horizontal U-shape with a terminal portion of the said U-shaped material extending beyond the corresponding posterior side in such a way as to be folded against the posterior side and overlapped at the folded terminal portion over the inferior face. This machine is provided with the conveyor constructed from two lengths of adjacent transporter sheet and the holding means supported opposite the zone consisting of the two adjacent lengths of sheet material and in which zone the contiguous zones of the two sheets pass round at least one corresponding pair of return rollers supported by an alternately moving carriage parallel to the direction of transport. The holding means are movable alternately vertically and parallel with respect to the movement of the carriage. Further, the machine was improved in other Italian Patent No. 1,186,646 has issued in the name of applicant of 11 Nov. 1985 and provided an improvement by implementing different means for feeding sheets cut from the sheet of heat-shrinking wrapping material across the line of movement of the articles to be wrapped and thereby improving the efficiency provided by the two adjacent lengths of transporter sheet.
Substantially, these different means for feeding the sheets of wrapping material comprise at least one pair of wrapping bars supported horizontally in continuous motion along a track surrounding the article which is to be wrapped in a continuous movement so that while one of the said bars wraps the wrapping material around a following article in the shape of a horizontal U on the anterior side and the two upper and lower sides of the following article, the other folds the terminal portion of the wrapping material onto the posterior side of the preceding article, so that the tail end of the terminal zone of material is folded back onto the underside above the initial zone of the improved contiguous lengths of transporter sheet thus achieving the maximum technological development of these machines now commercially available for continuous packaging using heat-shrinking sheet material in respect of both the quality of product obtained and greater productivity per unit time.